a) Field of the Invention
This invention relates to a process for producing colored fine particulate resins, colored fine particulate resins, and a process for coloring articles by using the colored fine particulate resins. More specifically, the present invention is concerned with the provision of a process for economically producing colored fine particulate resins, especially colored fine particulate resins useful as colorants for image recording materials such as developers for electrophotography and ink-jet printing inks, printing inks, powder coatings and slurry paints by production steps rationalized for mass production.
b) Description of the Related Art
A dry developer for electrophotography, which may hereinafter be called simply “a developer”, has conventionally be produced by so-called crush granulation, that is, by coarsely grinding a colored resin with a crusher or the like, finely grinding the coarsely-ground, colored resin with a mill such as a jet mill, and then removing coarse particles and dust with an air classifier. The colored resin can be obtained by metering, mixing and kneading a resin for the developer, a colorant and optional internal additives such as a charge control agent such that the colorant and optional internal additives are dissolved or dispersed in the resin.
It is proposed in JP 11-49864 A that in the above-described production process, production steps such as grinding of the resin, metering of the materials for each batch, and mixing in a tumbler or Henschel mixer can be improved by feeding the resin into an extruder, feeding the colorant and internal additives through automatic metering devices, and kneading the colorant and internal additives with the molten resin in the extruder.
The above-described crush granulation is, however, accompanied by a drawback in that production machines employed in the process, for example, a mill such as a jet mill and an air classifier are very expensive. On the other hand, developers have been finding increasing utility in various environments owing to popularization of office automation equipment. Keeping in step with this move, new requirements have arisen for developers, including use of a resin having a higher glass transition point as an anti-blocking measure and the like for improved storability; and changes of production conditions to meet the move toward developers of finer particle size, and more precise control of production conditions from the standpoint of a desire for image quality of higher definition.
This, however, has made it more difficult to produce a target product efficiently at low cost, because the need for feeding of the required components at controlled rates into a grinder and the need for providing the product with a smaller particle size and narrower particle size distribution have led to a reduction in productivity. Moreover, if these production conditions cannot be met by the existing equipment, an economical problem also arises in that a change to or introduction of new production machine or machines is needed. In addition, a developer produced by crush granulation is in the form of crushed particles of irregular shapes, and the distribution of surface charges is uneven. Compared with a spherical developer produced by suspension polymerization or the like, the production of a developer by crush granulation results in occurrence of residual dust in a greater amount, said residual dust being insufficient in performance as a developer, and is not economical.